This lighting model can be extended to accurately capture more complex lighting environments, with a number of arbitrarily placed light sources. As originally described in [1]}, [2]}, and forensically employed in [3]}, [4]}, [5]}, [6]}, under the assumption of distant lighting, the appearance of a convex Lambertian surface of constant reflectance can be modelled with a spherical Fourier basis. Specifically, a point on a surface with 3-D surface normal \(\vec{N}_k\) , is imaged to pixel location \(k\)  with pixel intensity given by:
\(\hspace{-14.22636pt}I_k & = & l_{0,0} \pi Y_{0,0}(\vec{N}_k) + \nonumber \\& & l_{1,-1} {\textstyle \frac{2\pi }{3}} Y_{1,-1}(\vec{N}_k) +l_{1,0} {\textstyle \frac{2\pi }{3}} Y_{1,0}(\vec{N}_k) +l_{1,1} {\textstyle \frac{2\pi }{3}} Y_{1,1}(\vec{N}_k) + \nonumber \\& & l_{2,-2} {\textstyle \frac{\pi }{4}} Y_{2,-2}(\vec{N}_k) +l_{2,-1} {\textstyle \frac{\pi }{4}} Y_{2,-1}(\vec{N}_k) +l_{2,0} {\textstyle \frac{\pi }{4}} Y_{2,0}(\vec{N}_k) +l_{2,1} {\textstyle \frac{\pi }{4}} Y_{2,1}(\vec{N}_k) + l_{2,2} {\textstyle \frac{\pi }{4}} Y_{2,2}(\vec{N}_k),\) 
